新疆洪古勒楞蛇绿岩套中堆积杂岩的地球化学特征及成因

新疆和布克赛尔蒙古族自治县境内的洪古勒楞蛇绿岩块,出露于西准噶尔海西褶皱带的西部。该蛇绿岩块的层序发育完好,尤其是保存了具有完整层序的堆积杂岩相。本文描述了堆积杂岩的矿物化学成分演化以及岩石化学、微量元素和稀土元素的地球化学变化规律,指出蛇绿岩、堆积杂岩具有层状镁铁超镁铁岩体的主要特点,两者在成因上是相似的。文中提出蛇绿岩、堆积杂岩是在岩浆房中经液态岩浆重力堆积形成的观点,并对液态堆积机制进行了解释。

GEOCHEMICAL CHARACTER AND ORIGIN OF CUMULATES OF THE HONGGULELENG OPHIOLITE, XINJIANG, CHINA

The cumulative complex is well preserved in the Hongguleleng ophiolitic suite located in the Hebukesai County, Xinjiang. The complex is consisted of the following sequences from bottom to top: 1) assemblage of plagioclase dunite and plagioclase harzburgite in iuterlayering, 2) metatroctolitic and leucotroctolitic interlayers as a rhythmic stratified structure,3)olivine gabbro and then homogeneous gabbro layer. The basic lava (diabase) layer is overlaid on the homogeneous gabbro layer. The andisitic basalt layer overlying on the ophiolitic suite may be cogenetic.The cumulative complex is typical of PTO assemblage and is characterized by an Al-rich evolution trend. The chemical compositions of the cumulates from the bottom to top have a tendenoy to increase in the CaO, Al2O3, SiO2, TiO2, Na2O, K2O, B and Sr, and decrease in the MgO, FeO, Cr, Co, and Ni. The chemical variations of major, trace and rare earth elements for the cumulates show the systematic change similar to those of the lavered mafic and ultramafic intrusions.In this paper, the authers suggest that the cumulative sequences are formed by liquid or magma accumulation and explain the mechanism of the liquid accumulation origin.